On January 28, the two men discussed how to defeat the Islamic State group in a congratulatory call from Putin, according to officials.

The last time, on April 3, Trump pledged support to Russia over a deadly bomb attack in the Saint Petersburg metro that killed 15 people.

US ties with Russia are under scrutiny after US intelligence agencies said hackers directed by the Kremlin accessed the Democratic National Committee networks ahead of the election that put Trump in the White House.

The FBI is probing any links between Trump campaign associates and the Russian government. The Pentagon is probing Trump’s former national security adviser, Michael Flynn, over payments received from Russian government-linked firms.